Reactive PLD Guides the Transformation to Noncrystalline C‐Ga‐Se‐Cl Films with a Halogen‐Defined Interface for Enhanced Luminescence

ABSTRACT

Pulsed laser deposition is known for copying the composition of a target into a thin film. Adding a reactive gas can change the growth process, but the chemistry usually stays close to the target. Using a carbon‑rich environment and a pulsed chlorine source from polyvinylidene chloride, we let a chalcogenide target transform into a completely different material during deposition. The result is an amorphous film dominated by a carbon network whose content rises from the bottom to the top, reaching 60 wt.%. Gallium, selenium, and chlorine are embedded in this carbon network, and a sharp interfacial layer about 40 nm thick appears where the chlorine was introduced in a short burst. This unusual structure gives the film an indirect optical bandgap of 3.175 eV, much larger than that of the original target materials. The film also shows strong broad‑spectrum photoluminescence in the 400–550 nm range. The luminescence comes from carbon clusters, chlorine‑related defects, and traps from selenium and sulfur. This work shows that reactive pulsed laser deposition can drive a complete chemical reconstruction of a target and create self‑assembled interfaces, offering a new way to design optical films with tailored bandgaps and emission properties.